Environmental Geology Chapter 3 CONTINENTAL TECTONICS

Environmental Geology Chapter 3 CONTINENTAL TECTONICS

Environmental Geology
Chapter 3
CONTINENTAL
TECTONICS
China University of Geosciences/Beijing
WORDS & MEANINGS TO KNOW
•
•
•
•
•
•
•
•
•
•
Geosyncline
Miogeosyncline (don’t use)
Eugeosyncline (don’t use)
Miogeocline
Eugeocline (don’t use)
Passive margin
Active margin
Subduction
Lithosphere
Asthenosphere
16,000,000 km of geophysical ocean
tracks by 1984 (US NOAA)
The 1950’s: Discoveries on
Ocean Topography and Seismicity
Gutenberg & Richter, 1954
The mid-ocean ridges and
rises are huge topographic
features!
Lamont-Doherty Observatory, New York:
Ocean Studies 1950’s and 1960’s
Mid-ocean “crack system”
(Maurice Ewing, late 1950’s)
Bruce Heezen, 1960
(after Hess, 1960)
Global Seismicity, 1961-1967
WHICH IS MOST IMPORTANT, BLACK OR WHITE?
Major earth plates
Our hemisphere
Plate Tectonics on a Sphere
Types of Plate Boundaries
Global (ocean + continents)
relief map
Plates on world relief map
Earth topo and plate
boundaries
Rates are in mm/year = kms/1,000,000
yrs
Plate Movement Vectors
Our hemisphere
Andean
Moho
Moho
Earth layers compositional & rheological
M =Mohorovicic
discontinuity
The Plate Tectonics Earth
THE OCEANIC LITHOSPHERE
IS FORMED AT SPREADING
RIDGES. IT THICKENS AWAY
FROM THEM AS THE
UNDERLYING
ASTHENOSPHERE COOLS
AND BECOMES
LITHOSPHERE
(SEE BELOW)
Magnetic anomalies found on ocean floor in
early 1960’s; their origin was unknown
NE Pacific
Ocean
Mid-Atlantic
Ridge
Reversals of Earth’s magnetic field are
captured by basaltic rocks formed during
sea-floor spreading at oceanic ridges
Reversals of Earth’s Magnetic Field During Spreading
Left: magnetic anomalies, NE Pacific (1961);
right: age of anomalies, Juan de Fuca ridge
Mid-Atlantic Ridge magnetic anomalies on
Reykjanes Ridge south of Iceland
RIDGE-RIDGE-RIDGE TRIPLE JUNCTIONS
Age of ocean basin floors
(crust)
RIDGE-RIDGE-RIDGE TRIPLE JUNCTIONS
Age of ocean basin floors
(crust)
RIDGE-RIDGE-RIDGE TRIPLE JUNCTIONS
Age of ocean basin floors
(crust)
Lava Lake Examples of Plate Tectonics:
Kilauea, Hawaii & Erte Ale, Afar, Africa
KILAUEA
LAVA LAKE AT
BOTTOM OF
PIT CRATER
SPREADING CENTERS
SUBDUCTION ZONE
OLDER CRUST BEING SEPARATED BY
YOUNGER SPREADING CENTER
OLDER CRUST BEING SEPARATED BY
YOUNGER SPREADING CENTER
TRANSFORM
FAULT
Erte Ale Volcano, Afar Triangle
ERTE ALE WITH SUMMIT CALDERA
PIT CRATER WITH LAVA LAKE
Dusk, pit illuminated by
lava fountain
Fountain and spreading
zones in pit
1 - EARLY
SPREADING
2 - DEAD SUBDUCTION ZONE
EARLY
SPREADING
DEAD SUBDUCTION ZONE
EARLY
SPREADING
3 - YOUNG, CROSS-CUTTING
SPREADING CENTER
DEAD SUBDUCTION ZONE
?
EARLY
SPREADING
3 - YOUNG, CROSS-CUTTING
SPREADING CENTER
Age of ocean basin floors
(crust)
MID-OCEAN RIDGES AND RISES AND
CONTINENTAL RIFTING
ARE NOT RELATED
TO MANTLE-WIDE
RISING AND SPREADING CONVECTION
CELLS
Plate Dynamics
OCEAN RIDGES ARE NOT STATIONARY
(THEY MIGRATE)
1
2
3
1
2
3